Apparatus and method for enabling communications among unsynchronized wireless devices

Abstract

A method enables a wireless device ( 310 ) to rendezvous with another wireless device ( 320 ) through a wireless network ( 330 ), where activation schedules of the wireless devices are not synchronized. The method includes determining a number of time units in each cycle of multiple communication cycles, identifying active time units in each cycle during which the first wireless device enters an active mode, and identifying inactive time units in each cycle during which the first wireless device enters an inactive mode. The sum of the active time units and the inactive time units equals the number of time units in each cycle. A first active time unit in each cycle occupies a same position in the cycle as an active time unit in a previous consecutive cycle. Also, a second active time unit in each cycle occupies a different position in the cycle than any active time unit in the previous consecutive cycle.

The invention claimed is: 
     
       1. A method of enabling a first wireless device to rendezvous with at least a second wireless device through a wireless network, where activation schedules of the first wireless device and the second wireless device are not synchronized, the method comprising:
 pre-determining by the first wireless device a number of time units in each cycle of a plurality of communication cycles; 
 creating an activation sequence having a plurality of active time units in each cycle during which the first wireless device enters an active mode and a plurality of inactive time units in each cycle during which the first wireless device enters an inactive mode, a sum of the plurality of active time units and the plurality of inactive time units equaling the number of time units in each cycle; and 
 controlling the creating such that a first active time unit of the plurality of active time units in each cycle occupies a same position in the cycle as an active time unit in a previous consecutive cycle, and a second active time unit of the plurality of active time units in each cycle occupies a different position in the cycle than any active time unit in the previous consecutive cycle. 
 
     
     
       2. The method of  claim 1 , wherein the second active time unit of the plurality of active time units in each cycle occupies a same position in the cycle as an active time unit in a subsequent consecutive cycle. 
     
     
       3. The method of  claim 2 , wherein the first active time unit of the plurality of active time units in each cycle occupies a different position in the cycle than any active time unit in the subsequent consecutive cycle. 
     
     
       4. The method of  claim 1 , wherein each time unit corresponds to a super-frame of the wireless network. 
     
     
       5. The method of  claim 4 , wherein the plurality of active time units in each cycle consists of the first active time unit and the second active time unit. 
     
     
       6. The method of  claim 5 , wherein creating the activation sequence having the plurality of active time units in each cycle comprises applying the following equation:
     X   i+1 =( X   i   +S )mod  C    
 wherein X i  is a value of the first active time unit, X i+1  is a value of the second active time unit, i is an integer, C is the number of time units in each cycle, and S is a constant having a value between 1 and C−1. 
 
     
     
       7. The method of  claim 6 , wherein the value of X i  of each cycle is equal to the value X i+1  of a previous consecutive cycle. 
     
     
       8. The method of  claim 1 , wherein the second wireless device:
 determines the number of time units in each cycle of a plurality of communication cycles; 
 creates an activation sequence having a plurality of active time units in each cycle during which the second wireless device enters an active mode and 
 a plurality of inactive time units in each cycle during which the second wireless device enters an inactive mode, a sum of the plurality of active time units and the plurality of inactive time units equaling the number of time units in each cycle, 
 wherein the creating by the second wireless device provides one of the plurality of active time units in each cycle occupying a same position in the cycle as an active time unit in a previous consecutive cycle, and 
 another active time unit of the plurality of active time units in each cycle occupies a different position in the cycle than any active time unit in the previous consecutive cycle. 
 
     
     
       9. The method of  claim 8 , wherein the first wireless device is able to communicate with the second wireless device when they are simultaneously in the active mode. 
     
     
       10. The method of  claim 1 , wherein the active mode comprises an awake mode during which the first wireless device awakens from a hibernation state and communicates over the wireless network. 
     
     
       11. The method of  claim 1 , wherein the active mode comprises a discovery mode during which the first wireless device performs a scan with a directional antenna for locating other directional antennas. 
     
     
       12. The method of  claim 11 , wherein the directional antenna scan comprises sweeping an antenna beam of the directional antenna. 
     
     
       13. A device for communicating over wireless network, configured to periodically rendezvous with at least one other device over the wireless network, where an activation schedule of the device is not synchronized with an activation schedule of the at least one other device, the device comprising:
 a memory for storing a rendezvous algorithm and information identifying a number of time units in each cycle of a plurality of cycles; and 
 a processor for creating an activation sequence having a plurality of active time units in each cycle, according to the rendezvous algorithm, during which the device enters an active mode, the activation sequence having a first active time unit of the plurality of active time units in each cycle occupy a same position in the cycle as an active time unit in a previous consecutive cycle, and a second active time unit of the plurality of active time units in each cycle occupy a different position in the cycle than any active time unit in the previous consecutive cycle, 
 wherein the device is in an inactive mode during a plurality of inactive time units of each cycle, a sum of the plurality of active time units and the plurality of inactive time units equaling the number of time units in each cycle. 
 
     
     
       14. The device of  claim 13 , wherein the rendezvous algorithm comprises the following, to determine the plurality of active time units in each cycle:
     X   i+1 =( X   i   +S )mod  C    
 wherein X i  is a value of the first active time unit, X i+1  is a value of the second active time unit, i is an integer, C is the number of time units in each cycle, and S is a constant having a value between 1 and C−1. 
 
     
     
       15. The device of  claim 14 , further comprising:
 a transceiver that is powered off during the inactive mode, 
 wherein the active mode comprises the transceiver awakening from the inactive mode and at least one of sending and receiving communications over the wireless network. 
 
     
     
       16. The device of  claim 15 , wherein the device has a duty cycle equal to a/C, where a is a number greater than 1 and less than C. 
     
     
       17. The device of  claim 14 , further comprising:
 an antenna for sending and receiving communication signals over the wireless network, 
 wherein the active mode comprises a discovery mode during which the antenna is used to locate an antenna of the at least one other device. 
 
     
     
       18. The device of  claim 17 , wherein the antenna comprises a directional antenna. 
     
     
       19. The device of  claim 14 , wherein the device is able to communicate with the at least one other device, which also executes the algorithm, when the device and the at least one other device are simultaneously in the active mode. 
     
     
       20. A method of enabling a first wireless device to rendezvous with a second wireless device over a wireless network, where activation schedules of the first wireless device and the second wireless device are not synchronized, the method comprising:
 determining two super-frames [X i , X i+1 ] in each cycle of a plurality of communication cycles, during which the first wireless device enters an active mode, according to the following equation, in which i is an integer, C is a number of super-frames in each cycle and S is a constant having a value between 1 and C−1:
     X   i+1 =( X   i   +S )mod  C,    
 
 
       and
 determining two super-frames [X′ i , X′ i+1 ] for each cycle during which the second wireless device enters an active mode, according to the following equation, in which S′ is a constant having a value between 1 and C−1 and S′ is not necessarily equal to S:
     X′   i+1 =( X′   i   +S ′)mod  C,  
 
 
 wherein the first wireless device and the second wireless device are able to at least one of locate and communicate with each other when both the first wireless device and the second wireless device are in the active mode simultaneously.